Bifacial modules generate electricity on both sides – at the front from direct light, at the back from light that is reflected by the surface below. The extra yield is worthwhile where a lot of light is reflected behind the modules and there is space: on flat roofs with a light surface, on open spaces or elevated. On the classic pitched roof, where the back is close above the tile, the advantage largely dissipates. (As of: July 2026)
Key points in brief
- Bifacial modules additionally use the light that falls on the back from behind.
- The extra yield depends on the surface below: light, reflective ground brings a lot, dark ground little.
- Ideal on flat roofs (elevated, light gravel) and open spaces – there is space and reflection there.
- On the classic pitched roof, the back lies too close to the tile: hardly any extra yield.
- Bifacial modules are always glass-glass modules – the transparent back is the prerequisite.
How does a module generate electricity on two sides?
A conventional module has a light-active front and an opaque back – electricity is only generated at the front. A bifacial module is also light-sensitive on the back: It has a transparent back made of glass through which light falls on the cells. Thus it not only uses the direct sunlight from the front, but also the light that is reflected from the surface behind the module.
Exactly for this reason bifacial modules are always glass-glass modules: Only the glass, translucent back lets the rear light through to the cells at all. A foil, as glass-foil modules have, would block it. The construction is therefore no coincidence, but the technical prerequisite for the two-sided yield.
What does the extra yield depend on?
Here lies the core of the honest classification: The extra yield of the back is not a fixed bonus, but depends completely on how much light arrives behind the module. And that is primarily decided by the surface below and the distance between module back and ground.
| Condition | Effect on the rear yield |
|---|---|
| light, reflective surface (light gravel, snow) | high |
| dark surface (dark roof, earth) | low |
| large distance back–ground (elevated) | promotes reflection |
| small distance (close above the tile) | hardly any rear light |
Simplified overview, as of: July 2026. The actual extra yield depends strongly on the installation situation.
The key figure behind this is called albedo – the reflectivity of the surface below. One does not have to know the term to understand the logic: A lot of reflected light means a lot of rear yield, little reflection means little. Therefore the decisive question with bifacial modules is never «how good is the module», but «what is behind it».
Regarding the order of magnitude: Investigations – among others by the Fraunhofer Institute for Solar Energy Systems – show extra yields from a few percent up to nearly 30 percent depending on the conditions. Realistic for a flat roof with a light surface is about 5 to 15 percent, over very light gravel even more; over dark surfaces hardly anything remains measurable (As of: July 2026). The large range is not a blur in the studies, but exactly the point: The surface below makes the difference.
Where bifacial modules shine – and where they dissipate
From this dependence follows a clear map of sensible uses.
Ideal on the flat roof. Elevated modules on a flat roof with a light surface – for example light gravel – are the prime case: The distance to the ground is there, the reflection is right, and the East-West or South elevation ensures the appropriate geometry anyway. Here the back can make a noticeable contribution.
Strong on open spaces and special applications. On open space systems, over light soils or in snowy locations (snow reflects strongly) bifacial modules play out their strength – they have long been widespread there. The special case of this construction is the vertical installation in the solar fence, where both sides of the module stand free.
Hardly on the classic pitched roof. And here the honest downside: On an ordinary pitched roof, the back of the module lies close above the tiles. Hardly any light gets behind it, the surface below is usually dark – the bifacial advantage largely dissipates. Whoever gets offered bifacial modules for a normal pitched roof with the promise of large extra yields should ask critically: The construction hardly brings its additional benefit to the street there. The more robust glass-glass structure can nevertheless be an argument – but because of the longevity, not because of the back.
Are bifacial modules worthwhile for my project?
The answer results from the roof, not from the data sheet. On a flat roof with suitable elevation and light surface, bifacial modules are worth serious consideration – the extra yield is real and the glass-glass construction, which is necessary anyway, brings longevity. On a normal pitched roof the case is different: Here the choice of module via cell type, orientation and quality counts more than the question of bifacial or not, because the rear yield hardly materialises due to lack of reflection.
The honest advice is therefore: Bifacial is not a general improvement that one should buy everywhere, but a technology for the suitable situation. A specialist company that knows your roof will tell you whether you belong to this situation – or whether the money is better spent in a classic, good module.
Bifacial modules are one of the topics where we have to brake most frequently – not because the technology is bad, on the contrary. But because it can hardly play out its advantage on the typical pitched roof that we cover the most. The back wants light, and behind a module that lies flat over the tiles, there is none. We then explain the rule of thumb that is easy to remember: Bifacial is worthwhile where there is space and a light surface behind the module – on the flat roof with light gravel, on the open space, over snow. On such a roof we are happy to recommend them with conviction. On the standard pitched roof, however, we advise putting the budget into an all-round good module instead, rather than paying for a back that lies in the dark. Good technology in the wrong place is not a good purchase.
Frequently asked questions
What are bifacial solar modules?
Modules that generate electricity on both sides: at the front from direct sunlight, at the back from light that is reflected from the surface below. For this they have a transparent glass back. The extra yield of the back depends heavily on how much light arrives behind the module.
How much extra yield do bifacial modules bring?
Varies greatly depending on the installation situation: on a flat roof with a light background, around 5 to 15 percent is realistic, even more over very light gravel – studies show up to around 30 percent under optimal conditions. In contrast, close to a dark pitched roof, the contribution remains minimal. The installation situation is the deciding factor, not the module alone.
Are bifacial modules worthwhile on a pitched roof?
Usually not. On a classic pitched roof, the back is too close to the (often dark) tiles – hardly any light gets behind them, and the bifacial advantage fizzles out. They are mainly useful on flat roofs with a light background, in open spaces and in snow-rich areas.
Why are bifacial modules always glass-glass?
Because the back must let light through so that electricity can be generated there. Only a glass, transparent back can do this – a plastic film would block the light. The glass-glass design is therefore the technical prerequisite for the two-sided yield.
Are bifacial modules more expensive?
They are glass-glass modules and therefore tend to be priced above simple glass-foil modules. Whether this is worthwhile depends on the location: where the rear-side yield is achieved, the surcharge can make sense; where it fizzles out, you pay for an advantage that you do not harvest.
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Bifacial or classic – what does your roof yield?
We assess whether your roof can produce the two-sided yield at all – and only recommend bifacial modules where they really play out their advantage.
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Swissolar-certified specialist company · ESTI installation authorisation (Art. 14 NIV) · in Zurich since 2017 · over 150 systems completed · a personal answer from the specialist company, no call centre
Sources: Fraunhofer Institute for Solar Energy Systems ISE (studies on bifacial additional yield); manufacturer documentation (bifacial modules and albedo influence); Swissolar; empirical values from the planning and installation practice of ecoEn GmbH, Zurich region. (As of: July 2026)
Last updated: 9 July 2026 · Author: ecoEn editorial team
